Welding contact tips for use in automatic arc welding or semi-automatic arc welding have a wire passage for feeding a welding wire which is formed in the center of a shaft-like member formed of usually copper alloy which is a conductive material. The welding wire is passed through the wire passage. Arc welding is conducted at an end of the welding wire which is being supplied.
Meanwhile, the front end of the welding contact tip is exposed to high temperatures at the time of arc welding, therefore it is seriously worn. Because the welding wire is supplied through the wire passage, a shape of the passage at a front opening portion is inclined to change from its original circular shape to an oval shape due to abrasion between the welding wire and the passage. If the shape of the front opening portion of the wire passage is deformed, supply of the welding wire to a welding portion becomes unstable. Consequently, the wire is deviated from its proper position so that favorable arc welding is disabled. Additionally, spatter or the like substance easily sticks to walls of the wire passage thereby making it difficult to conduct welding operation.
Thus, various technologies were proposed to solve the above problem since before. For example, as shown in Japanese Utility Model Laid-Open No.Sho60-20372 and Japanese Utility Model Laid-Open No.Sho62-169774, a ring made of abrasion resistant material is forced into or sealed into the front end of the welding contact tip subjected to severe wearing. Japanese Patent Laid-Open No.Sho61-115683 and Japanese Patent Laid-Open No.Sho63-188477 have disclosed technologies for covering a front end portion of the contact tip with ceramic cap. Japanese Patent Laid-Open No.Hei6-285645 has disclosed a technology of coating a surface of the contact tip with heat resistant resin. Japanese Patent Laid-Open No.Hei5-261551 has disclosed a technology in which the end portion of the contact tip is structured in double tubes while an inside wire passage portion is of ceramic tube. Japanese Patent Laid-Open No.Hei5-277742 and Japanese Patent Laid-Open No.Hei6-650 have disclosed technologies in which entire contact tip is constructed with double tubes.
The technologies of forcing or sealing the abrasion resistant material into the welding contact tip, disclosed in the Japanese Utility Model Laid-Open No.Sho60-20372 and Japanese Utility Model Laid-Open No.Sho62-169774 have such a problem that cracks, loosening or the like is likely to occur at a portion in which a ring is forced in or sealed in. Further those technologies take trouble in production and do not produce excellent production performance (accuracy). The technologies of covering the front end of the contact tip with ceramic cap disclosed in the Japanese Patent Laid-Open No.Sho61-115683 and Japanese Patent Laid-Open No.Sho63-188477 and the technology of coating the surface of the contact tip with heat resistant resin disclosed in Japanese Patent Laid-Open No.Hei6-285645 are effective for preventing spatter from being adhered to the contact tip surface to some extent, however are not capable of solving fundamental problems such as deformation of the wire passage and wearing, and are limited in terms of improvement of durability. Thus those technologies are not practically usable.
Further, the technologies of providing double tube structure to raise the durability of the wire passage disclosed in Japanese Patent Laid-Open No.Hei5-261551 and Japanese Patent Laid-Open No.Hei5-277742 have such a problem that production methods are complicated and take troubles thereby increasing production cost. Thus, these technologies have not been realized for actual application.